1. Field of the Invention
The present invention relates to a method for testing hydrostatic pressure of various kinds of inflators in which a pressurized medium, such as an inert gas, is charged under a high pressure, and a method for manufacturing such various kinds of inflators.
2. Description of Related Art
In an air bag apparatus mounted to an automobile or the like, an inflator which inflates an air bag by an inert gas charged under a high pressure therein or the like, is incorporated. In an inflator of this type, an inert gas such as argon, helium is charged at a high pressure into an inflator housing constituting an outer shell container. Therefore, it is required to test hydrostatic pressure on all products and confirm their safety by the law (High Pressure Gas Safety Law) to secure safety of passengers.
In such a test method, it is required to apply pressure of 1.5 times the internal pressure in an actual product to evaluate the safety thereof. When the charging pressure is 50 to 60 MPa, the hydrostatic pressure in the test is required to be under the high pressure of 75 to 90 MPa. Conventionally, as a method for conducting such a test, the steps of charging gas into an inflator housing and pressurizing the same, or the steps of injecting oil having a high viscosity into an inflator housing and pressurizing the same are employed.
However, in case of charging a gas under a high pressure, a device for charging the gas under such a high pressure is very expensive, and also, if there is a defect, such as bad welding, an inflator housing may break violently due to a gas leakage and may injure a worker.
Also, in case of injecting an oil having a high viscosity, although the safety at a time of the test is high, it is difficult to clean and dry the inside of the inflator housing after the oil is removed, a gas for inflating an air bag is polluted by the remaining oil, and the remaining oil may adversely affect a welded portion.
Further, it is preferable that the testing of hydrostatic pressure is not performed independently of inflator manufacturing processes but incorporated in the manufacturing processes. Therefore, it is also required that a smooth flow of manufacturing processes is not obstructed in view of the whole manufacturing procedure.